I agree with the other opinions that this is a Great Cormorant. The white head and white flank patch are indications of breeding plumage (the dark behind the eye is also typical of this plumage). Your concerns about the greyer wings and tail are a result of the photograph (the light is reflecting off these areas). The size in relation to the egrets in the larger picture looks fine.
Compared to Eastern Marsh Harrier, the bird is not the right colour (black rather than brown), has a longer bill (a yellow bill is apparent on this photo) and is wrong in terms of structure. The location and habitat is also unlikely for harriers. The only possible confusion in my opinion is Japanese Cormorant, which cannot be ruled out on these photos but is highly unlikely.
